1. Field of the Invention
Embodiments of the present disclosure are directed towards steel compositions that provide good toughness under corrosive environments. Embodiments also relate to protection on the surface of the steel, reducing the permeation of hydrogen. Good process control, in terms of the heat treatment working window and resistance to surface oxidation at rolling temperature, are further provided.
2. Description of the Related Art
The insertion of hydrogen into metals has been extensively investigated with relation to energy storage, as well as the degradation of transition metals, such as spalling, hydrogen embrittlement, cracking and corrosion. The hydrogen concentration in metals, such as steels, may be influenced by the corrosion rate of the steel, the protectiveness of corrosive films formed on the steel, and the diffusivity of the hydrogen through the steel. Hydrogen mobility inside the steel is further influenced by microstructure, including the type and quantity of precipitates, grain borders, and dislocation density. Thus, the amount of absorbed hydrogen not only depends on the hydrogen-microstructure interaction but also on the protectiveness of the corrosion products formed.
Hydrogen absorption may also be enhanced in the presence of absorbed catalytic poison species, such as hydrogen sulfide (H2S). While this phenomenon is not well understood, it is of significance for High Strength Low Alloy Steels (HSLAs) used in oil extraction. The combination of high strength in the steels and large quantities of hydrogen in H2S environments can lead to catastrophic failures of these steels.
From the forgoing, then, there is a continued need for steel compositions which provide improved resistance to corrosion in aggressive environments, such as those containing H2S.